We study the effect of public insurance for children on their utilization of medical care and health outcomes by exploiting recent expansions of the Medicaid program to low-income children. These expansions doubled the fraction of children eligible for Medicaid between 1984 and 1992. Take-up of these expansions was much less than full, however, even among otherwise uninsured children. Despite this take-up problem, eligibility for Medicaid significantly increased the utilization of medical care, particularly care delivered in physicians' offices. Increased eligibility was also associated with a sizable and significant reduction in child mortality.